U.S. patent application number 13/277071 was filed with the patent office on 2013-04-25 for inter-area oscillation detection.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is Jorge Eduardo Cardenas Medina, llia Voloh, Zhiying Zhang. Invention is credited to Jorge Eduardo Cardenas Medina, llia Voloh, Zhiying Zhang.
Application Number | 20130100564 13/277071 |
Document ID | / |
Family ID | 48135788 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130100564 |
Kind Code |
A1 |
Zhang; Zhiying ; et
al. |
April 25, 2013 |
INTER-AREA OSCILLATION DETECTION
Abstract
A device includes interface circuitry. The interface circuitry
receives first input signals related to measurements of
characteristics of electricity passing through a first power line.
The device includes filtering circuitry that filters the first
input signals to generate filtered data. The device also includes a
processor that estimates an oscillation frequency of the filtered
data via a time-domain frequency estimation method.
Inventors: |
Zhang; Zhiying; (Ontario,
CA) ; Voloh; llia; (Ontario, CA) ; Cardenas
Medina; Jorge Eduardo; (Guadalajara, ES) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zhang; Zhiying
Voloh; llia
Cardenas Medina; Jorge Eduardo |
Ontario
Ontario
Guadalajara |
|
CA
CA
ES |
|
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
48135788 |
Appl. No.: |
13/277071 |
Filed: |
October 19, 2011 |
Current U.S.
Class: |
361/78 ;
324/76.13 |
Current CPC
Class: |
H02H 7/28 20130101; H02H
3/048 20130101; H02H 3/046 20130101 |
Class at
Publication: |
361/78 ;
324/76.13 |
International
Class: |
H02H 3/00 20060101
H02H003/00; G01D 1/14 20060101 G01D001/14 |
Claims
1. A system, comprising: a master relay configured to: sample input
signals related to measurements of characteristics of electricity
passing through a power line; estimate an oscillation frequency of
the sample input signals via a time-domain frequency estimation
method; and estimate an oscillation magnitude of the sample input
signals via an adjusted window Fourier transform calculation based
on the estimated oscillation frequency.
2. The system of claim 1, wherein the master relay is configured to
transmit an alarm based on a comparison between the estimated
oscillation magnitude and a predetermined threshold value.
3. The system of claim 1, wherein the master relay is configured to
transmit a trip signal to interrupt power transmission on the power
line based on a comparison between the estimated oscillation
magnitude and a predetermined threshold value.
4. The system of claim 1, wherein the master relay comprises
interface circuitry configured to interrupt power transmission on
the power line based on a comparison between the estimated
oscillation magnitude and a predetermined threshold value.
5. The system of claim 1, wherein the time-domain frequency
estimation method comprises estimating a raw frequency of an
oscillation to be determined, calculating an average frequency of
the oscillation, and determining a total number of samples for a
full oscillation period.
6. The system of claim 1, comprising a slave relay configured to:
sample second input signals related to measurements of
characteristics of electricity passing through a second power line;
and transmit the second sample input signals to the master
relay.
7. A non-transitory computer readable medium, comprising
computer-readable instructions to: receive input signals related to
measurements of characteristics of electricity passing through a
power line; validate the input signals; and estimate an oscillation
frequency of the input signals via a time-domain frequency
estimation method.
8. The non-transitory computer readable medium of claim 7,
comprising computer readable instructions to estimate an
oscillation magnitude of the sample input signals via an adjusted
window Fourier transform calculation based on the estimated
oscillation frequency.
9. The non-transitory computer readable medium of claim 8,
comprising computer readable instructions to generate an alarm
signal based on a comparison between the estimated oscillation
magnitude and a predetermined threshold value.
10. The non-transitory computer readable medium of claim 8,
comprising computer readable instructions to generate a trip signal
to interrupt power transmission on the power line based on a
comparison between the estimated oscillation magnitude and a
predetermined threshold value.
11. The non-transitory computer readable medium of claim 7, wherein
validating the input signals comprises confirming that the input
signals fall within a range of pre-determined frequencies.
12. The non-transitory computer readable medium of claim 7, wherein
validating the input signals comprises confirming that the
consecutive positive alternating current (AC) samples exceed an
upper threshold and consecutive negative AC samples exceed a lower
threshold.
13. The non-transitory computer readable medium of claim 7, wherein
validating the input signals comprises determining whether input
signals from a period previous to a current period have been
oscillatory.
14. The non-transitory computer readable medium of claim 7, wherein
the time-domain frequency estimation method comprises
computer-readable instructions to: estimate a raw frequency of an
oscillation to be determined; calculate an average frequency of the
oscillation; and determining a total number of samples for a full
oscillation period.
15. A device, comprising: interface circuitry configured to receive
first input signals related to measurements of characteristics of
electricity passing through a first power line; filtering circuitry
configured to filter the first input signals to generate filtered
data; and a processor configured to estimate an oscillation
frequency of the filtered data via a time-domain frequency
estimation method.
16. The device of claim 15, wherein the processor is configured to
generate an estimate an oscillation magnitude of the filtered data
via an adjusted window Fourier transform calculation based on the
estimated oscillation frequency.
17. The device of claim 16, wherein the processor is configured to
generate an alarm signal or a trip signal based on a comparison
between the estimated oscillation magnitude and a predetermined
threshold value.
18. The device of claim 17, comprising a network interface circuit
configured to transmit the alarm signal or the trip signal.
19. The device of claim 15, comprising a network interface circuit
configured to receive second input signals related to measurements
of characteristics of electricity passing through a second power
line.
20. The device of claim 19, wherein the filtering circuitry is
configured to filter the second input signals with the first input
signals to generate the filtered data.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to detection of
inter-area low frequency oscillations in power lines.
[0002] Modern power systems are becoming increasingly
interconnected to each other for the benefits of increased
reliability, reduced operation cost, improved power quality, and
reduced necessary spinning reserve. However, the interconnected
power systems may also bring some technical challenges. Of them,
inter-area low frequency oscillations have become one of the major
threats to reliable operations of large-scale power systems.
Inter-area oscillations may occur when large synchronously
interconnected power systems have rotor
angle/frequency/power/voltage/current swings between the
synchronous generators of a first subsystem (or of large power
plant) and another subsystem (or other subsystems).
[0003] Inter-area oscillations not only limit the amount of power
transfer, but also threaten the system security, because they may
lead to system instability, which may result in cascading outages
in the system. Therefore, it is desirable to identify the
characteristics of the inter-area oscillations, including
oscillation frequency and damping ratio, so that proper actions can
be taken based on the identification results to improve system
damping and maintain system stability.
BRIEF DESCRIPTION OF THE INVENTION
[0004] Certain embodiments commensurate in scope with the
originally claimed invention are summarized below. These
embodiments are not intended to limit the scope of the claimed
invention, but rather these embodiments are intended only to
provide a brief summary of possible forms of the invention. Indeed,
the invention may encompass a variety of forms that may be similar
to or different from the embodiments set forth below.
[0005] In one embodiment, a system includes a master relay
configured to sample input signals related to measurements of
characteristics of electricity passing through a power line,
estimate an oscillation frequency of the sample input signals via a
time-domain frequency estimation method, and estimate an
oscillation magnitude of the sample input signals via an adjusted
window Fourier transform calculation based on the estimated
oscillation frequency.
[0006] In a second embodiment, a non-transitory computer readable
medium includes computer-readable instructions to receive input
signals related to measurements of characteristics of electricity
passing through a power line, validate the input signals, and
estimate an oscillation frequency of the input signals via a
time-domain frequency estimation method.
[0007] In a third embodiment, a device, includes interface
circuitry configured to receive first input signals related to
measurements of characteristics of electricity passing through a
first power line, filtering circuitry configured to filter the
first input signals to generate filtered data, and a processor
configured to estimate an oscillation frequency of the filtered
data via a time-domain frequency estimation method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0009] FIG. 1 is a block diagram of a power transmission system, in
accordance with an embodiment;
[0010] FIG. 2 is a is a block diagram of a master relay of the
power transmission system of FIG. 1, in accordance with an
embodiment; and
[0011] FIG. 3 is flow diagram illustrating steps undertaken by the
master relay of FIG. 2 to determine inter-area low frequency
oscillations in power lines of the power transmission system of
FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0012] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, all features of an actual
implementation may not be described in the specification. It should
be appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0013] When introducing elements of various embodiments of the
present invention, the articles "a," "an," "the," and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements.
[0014] Present embodiments relate to an inter-area oscillation
detection system that may incorporate a small signal oscillation
detector (SSOD). This SSOD may be implemented, for example, in one
or more relays positioned in a power transmission system. The
relays, utilizing the SSOD, may estimate an oscillation frequency
and an oscillation magnitude on a given power line. Any SSOD may
operate to provide alert to system operators or to cause a
separation in the interconnected system (e.g., trip or interrupt
the system) when a persistent or an unstable oscillation occurs.
Additionally, the SSOD may utilize real time measured analog
quantities, for example frequency or real power on the power lines
between different power systems to make determination if an alarm
or trip signal should be issued. Furthermore, the measured data may
come from a local relay alone, or from one or more remote
relays.
[0015] With the foregoing in mind, FIG. 1 represents a power
transmission system 100. The system 100 may include a first power
generation system 102 and a second power generation system 104.
Each of the power generation systems 102 and 104 may represent one
or more power plants powered by, for example, nuclear fission,
burning of fossil fuels (such as coal or natural gas), wind, solar
energy, or the like. It should be noted that the power generation
systems 102 and 104 may be separated by, for example, 50 miles, 100
miles, 200 miles, or more. In another embodiment, each of the power
generation systems 102 and 104 may reside in differing regions such
as different states, provinces, countries, or the like.
Accordingly, power generation system 102 may generate electricity
that includes differing characteristics (voltage, current, etc.)
than the electricity generated at power generation system 104,
based on, for example, the requirements and/or regulations of a
particular region in which the power generation systems 102 and 104
are located.
[0016] Power generation systems 102 and 104 may each generate
electricity to be transmitted across power lines 106, 108, 110,
112, and 114 (e.g., high voltage power lines). These power lines
106, 108, 110, 112, and 114 may transmit electricity at voltages,
for example, of 110 kV or greater to substations 116 and 118,
which, for example, may include step-down transformers, to reduce
the voltage of the electricity received. This stepped-down voltage
may then be distributed to customers, for example, along
distribution lines 120 and 122.
[0017] Additionally, the power transmission system 100 may include
relays, such as master relay 124 and slave relays 126a and 126b.
Each of the master relay 124 and the slave relays 126a and 126b may
operate to monitor a particular power line, power line 108, 112,
and 114, respectively, to detect inter-area low frequency
oscillations caused by, for example, power generation systems 102
and 104 transmitting power in a non-synchronous manner. This
monitoring may occur via interface circuitry 128 that may be
coupled (externally or internally) to each of the master relay 124
and the slave relays 126a and 126b. That is, the interface
circuitry 128 may detect disturbances in the electricity passing
through the power lines, for example, power lines 108, 112, and
114, that may then be utilized by the master relay 124 and the
slave relays 126a and 126b to detect inter-area low frequency
oscillations.
[0018] In one embodiment, a single master relay 124 may receive
measurements relating to inter-area low frequency oscillations from
a single one of the slave relays 126a and 126b. In another
embodiment the master relay 124 may receive measurements relating
to inter-area low frequency oscillations from more than one of the
slave relays 126a and 126b, for example, two, three, four, five, or
more slave relays. Additionally or alternatively, each of the
master relay 124 and the slave relays 126a and 126b may
independently determine if inter-area low frequency oscillations
are occurring on its monitored power line (e.g., power lines 108,
112, and 114, respectively) independently from any other
relays.
[0019] When measurements from other relays are utilized, for
example, when master relay 124 receives information relating to
inter-area low frequency oscillations on line 112 from slave relay
126a or information relating to inter-area low frequency
oscillations on line 114 from slave relay 126b, this information
may be received along communication channels 130a and 130b. In one
embodiment, communication channels 130a and 130b may be an
International Electrotechnical Commission's (IEC) 61850 standard
communication link. Additionally or alternatively, the
communication channels 130a and 130b may utilize a known wired
communication channel, such as an Ethernet connection, or may
utilize a known wireless communication channel, such as a wide area
network or a local area network, to transmit information between,
for example, slave relay 126a and master relay 124.
[0020] FIG. 2 illustrates an embodiment of the master relay 124. In
one embodiment, each of the slave relays 126a and 126b may include
substantially all of the same components as will be discussed below
with respect to master relay 124. Master relay 124 may include one
or more processors 132 and/or other data processing circuitry that
may be operably coupled to a memory 134 and storage 136 to execute
instructions for carrying out the presently disclosed techniques.
These instructions may be encoded in programs that may be executed
by the one or more processors 132. The instructions may be stored
in any suitable article of manufacturer that includes at least one
tangible non-transitory, computer-readable medium that at least
collectively stores these instructions or routines, such as the
memory 134 or the storage 136.
[0021] The processor(s) 132 may provide the processing capability
to execute an operating system, programs, and/or any other
functions of the master relay 124. In one embodiment, the
processor(s) 132 may operate to run a small signal oscillation
detector (SSOD). The SSOD may be an algorithm, stored on a tangible
machine readable medium such as memory 134 and or storage 136, that
may include steps or functions performed by the processor(s) 132.
These steps or functions may allow for estimation of an oscillation
frequency and an oscillation magnitude on one or more given power
lines (e.g., power line 108) to aid in preventing inter-area low
frequency oscillations.
[0022] The processor(s) 132 may include one or more
microprocessors, such as one or more "general-purpose"
microprocessors, one or more special-purpose microprocessors and/or
ASICS, or some combination thereof. Furthermore, as noted above,
instructions or data to be processed by the processor(s) 132 may be
stored in a computer-readable medium, such as a memory 134. Memory
134 may include volatile memory, such as random access memory
(RAM), and/or as a non-volatile memory, such as read-only memory
(ROM). Memory 134 may, for example, store firmware for the master
relay 124 (such as a basic input/output instructions or operating
system instructions), as well as various programs, applications, or
routines executable by the processor(s) 132 in the master relay 124
(e.g., the SSOD).
[0023] As previously noted, master relay 124 may also include
computer-readable media, such as storage 136. Storage 136 may
include non-volatile storage for persistent storage of data and/or
instructions. In one embodiment, the storage 136 may include flash
memory, a hard drive, solid-state storage media, or any other known
non-volatile media. The master relay 124 may also include
input/output (I/O) ports 138 for connection to external devices
(e.g., a portable computer, etc.) so that on site diagnostics
and/or repairs of the master relay 124 may be accomplished.
[0024] Furthermore, the master relay 124 may include a network
interface 140. The network interface 140 may provide communication
via a wireless network, such as a local area network (LAN) (e.g.,
Wi-Fi), a wide area network (WAN) (e.g., 3G or 4G), or a physical
connection, such as an Ethernet connection, an IEC 61850 standard
communication link, and/or the like. In one embodiment, the network
interface 140 may receive signals from one or more of the slave
relays 126a and 126b relating to measurements for determination of
inter-area low frequency oscillations on the power lines (e.g.,
power lines 112 and 114) that the slave relays 126a and 126b
monitor.
[0025] Additionally the master relay 124 may include conversion
circuitry 142. This conversion circuitry 142 may be utilized to
receive measurements relating to oscillations in the power passing
through a power line, for example, power line 108. Accordingly,
conversion circuitry 142 may include the interface circuitry 128
from FIG. 1 or the interface circuitry 128 may be coupled thereto.
Additionally, the conversion circuitry 142 may include one or more
filtering circuits 144 and an analog to digital (A/D) converter
circuit 146. The one or more filtering circuits 144 may filter
signals received from the interface circuitry 128, for example, to
operate as an anti-aliasing filter, a band pass filter, or the
like. The A/D converter circuit 146 may operate on the filtered
signals, for example, to produce digital signals that may be
utilized by the processor(s) 132 in conjunction with the SSOD
program to allow for estimation of an oscillation frequency and/or
an oscillation magnitude on one or more given power lines. FIG. 3
illustrates steps that are undertaken to estimate inter-area low
frequency oscillations utilizing, for example, the SSOD program as
executed in the master relay 124 of FIG. 2.
[0026] FIG. 3 is a flow diagram 148 illustrating the steps
undertaken to detect and alert of the presence of inter-area low
frequency oscillations in real time. In step 150, data may be
received, for example, at the master relay 124 from the slave
relays 126a and 126b. As previously noted, this data may be
received through the network interface 140 of the master relay 124
from communication channels 130a and 130b. Additionally or
alternatively, the data may be received in step 150 from the
interface circuitry 128 of the master relay 124.
[0027] In step 152, the data received in step 150 may be aligned
and consolidated. Step 152 may include, for example, alignment and
configuration of real power data and/or frequency data that are to
be used as input signals (data values) to the SSOD program.
However, other signals may be used, such as voltage, current,
reactive power, angle differences, etc. In one embodiment,
utilization of frequency signals may allow for measurement to be
undertaken locally (e.g., at the master relay 124) without
requiring data from the slave relays 126a and 126b. This may lead
to computational efficiencies, as less overall data is utilized by
the SSOD. In contrast, for example, when real power data is
utilized as the input signal to the SSOD, data from the slave
relays 126a and 126b (as well as any other slaves present in the
system 100) may be utilized in conjunction with data from the
master relay.
[0028] Regardless of the signals chosen for use as inputs to the
SSOD program, data may be captured at a fixed sample rate, for
example, every 10 ms, 20 ms, 50 ms, 100 ms, or at another rate.
Data synchronization may be performed on the sampled data via, for
example, the processor(s) 132 using linear interpolation based on a
timestamp, with the synchronized data being subsequently stored in
an alignment buffer, for example, in memory 134. Moreover, data
that is received outside of a particular timeslot, for example,
past 1/3 of the interval selected (e.g., 33 ms for a 100 ms
interval) is discarded as invalid as part of the synchronization
process.
[0029] In one embodiment, if two consecutive measurements are
invalid (e.g., if the data is received outside of a particular
timeslot), then data stored to that point is reset and the SSOD
element is blocked until a set of consecutive valid measurements
(e.g. data) are received (e.g., valid data received for 5 seconds,
10 seconds, 20 seconds, etc.). In this manner, the data is aligned
(via the time it is received) and consolidated (by grouping any
received data from a given time into a particular set) during step
152. Furthermore, it should be noted that the alignment and
consolidation step 152 may be performed by the SSOD program being
run on the processor(s) 132.
[0030] Once the data has been aligned and consolidated in step 152,
the data may be filtered and validated in step 154. For example,
filtering may be accomplished by the filtering circuits 144. This
filtering in step 154 may include removing a direct current (DC)
component from the data signals (as the subsequent oscillation
detection and validation checks may be based on alternating current
(AC) components of the signals). The filtering in step 154 may also
include passing the data through a low pass filter in the filtering
circuits 144 to eliminate high frequency noise elements in the
data.
[0031] The filtered data may also be validated in step 154. For
example, as the in-band frequency (e.g., the possible inter-area
oscillation frequency range) may be 0.1 Hz to 1.0 Hz, it may be
helpful to confirm (i.e., validate) that the data signals fall
within this range of in-band frequencies. To validate that the data
signals are in the correct frequency band, a time domain validation
check may be utilized that determines whether the low pass filtered
data signals lie within the correct in-band frequencies. Additional
validations such as dead band checking, to determine whether
consecutive positive AC samples exceed an upper dead band threshold
and consecutive negative AC samples exceed a lower dead band
threshold may be performed. The dead band thresholds may include
tolerance levels for the steady state operation of the sample
signals (e.g., whether the samples are within a preset tolerance).
This dead band checking may prevent the SSOD algorithm from
proceeding when low magnitude noises (oscillations in the sample
data) are present.
[0032] Further validation may be undertaken in step 154. For
example, a past period validation may be undertaken by the SSOD
program in step 154. This past period validation may include
determining whether samples for a previous period have been
oscillatory in nature, e.g., that the input signal in the past
period has included positive samples followed by consecutive
negative samples followed by consecutive positive samples. Also
verified is that the number of consecutive positive samples and the
number of consecutive negative samples are within the expected
limit. If each of these validations are confirmed by the SSOD, step
156 is undertaken.
[0033] In step 156, a frequency estimation for a inter-area low
frequency oscillation is undertaken. For example, a time-domain
frequency estimation method may be applied to estimate the raw
frequency of the oscillation to be determined This may be estimated
by using the following equation:
f(n)=1/(2.pi.kTs)*arcos
{0.5*[u(n-2k)*u(n-k)-u(n)*u(n-3k)]/[u(n-k)*u(n-k)-u(n)*u(n-2k)]}
[0034] Additionally, the average frequency of the oscillation may
be calculated by the following equation:
favg(n)=(1/N)*(f(n)+f(n-1)+ . . . +f(n-N+1))
[0035] Furthermore, the total number of samples for a full
oscillation period may be calculated by the equation:
Nm=integer(fs/favg(n))
[0036] In the above referenced equations, u is the input signal
after the process of alignment, consolidation, filtering and
validation, f is the estimated raw frequency of the oscillation,
favg is the N point average of f, n is the sample index, Ts is the
sampling interval, N is the total number of samples in one
oscillation period, and k is a number of sample delays. Moreover,
both N and k may vary in run time such that, for example, in each
loop of running the SSOD program, if N<Nm, the N is increased by
1 whereas if N>Nm, N is decreased by 1, and k is set to the
maximum value between N/12 and 3. Through the use of these
equations, the oscillation magnitude may be estimated in step
158.
[0037] That is, once the oscillation frequency is estimated, N
(i.e. the total number of samples in one oscillation period) is
known accordingly. Thus, the oscillation magnitude may then be
calculated in step 158 by using an adaptive window length full
cycle Fourier transform, i.e. a Fourier transform window length
will follow the change of number N. Thus, the window length (e.g.,
amount of data to be operated on) in the Fourier transform may be
adjusted based on the estimated oscillation frequency that has been
determined. Accordingly, the full cycle N points Fourier transform
calculation is defined below:
Cp=cos(2.pi.p/N)
Sp=-sin(2.pi.p/N)
UC(n)=(2/N)*SUM(u(n-p+N+1)*Cp)
US(n)=(2/N)*SUM(u(n-p+N+1)*Sp)
Umag(n)=sqrt(UC(n) 2+US(n) 2)
[0038] In the above referenced equations, p=0, 1, 2, . . . , N-1,
SUM is the summation of each term inside the bracket of the SUM,
and Umag is the estimated oscillation magnitude. Through the use of
these equations, the estimated oscillation magnitude may be
realized by the SSOD program. Moreover, based on the estimated
oscillation magnitude determined in step 158, an alarm and/or trip
decision may be made by the SSOD program in step 160.
[0039] In step 160, the SSOD program may determine if the estimated
oscillation magnitude determined in step 158, for example, exceeds
a predetermined alarm threshold value. If the predetermined alarm
threshold is exceeded, the SSOD program may trigger an alarm signal
to be sent in step 160, for example, to one or both of the power
generation systems 102 and 104. In one embodiment, this alarm may
be transmitted via the network interface 140 of the master relay
124. This alarm may indicate that inter-area low frequency
oscillations have been detected and may signal the power generation
systems 102 and 104 that problems due to inter-area low frequency
oscillations are impending.
[0040] Additionally or alternatively, in step 160, the SSOD program
may determine if the estimated oscillation magnitude determined in
step 158, for example, exceeds a predetermined trip threshold
value. This trip threshold value may be the same value as or may
differ from the value of the predetermined alarm threshold. If the
predetermined trip threshold is exceeded, the SSOD program may
trigger a trip signal to be sent in step 160, for example, to one
or both of the power generation systems 102 and 104. In one
embodiment, this trip signal may be transmitted via the network
interface 140 of the master relay 124. This trip signal may
indicate that inter-area low frequency oscillations have been
detected and may signal the power generation systems 102 and 104
that problems are impending and that at least one of the power
lines (e.g., power line 108) should be tripped (e.g., reset). In
another embodiment, the master relay 124 may itself trip the power
line (e.g., power line 108) via, for example, the interface
circuitry 128.
[0041] This written description uses examples to disclose the
invention, including the best mode, and also to allow any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *